CONTRA COSTA COUNTY (KRON) — A deadly mushroom has sprouted at a popular Contra Costa County Park, killing at least one dog.

The mushroom is known as a “death cap.”

If your dog eats one of these mushrooms and doesn’t get immediate treatment, the outcome is likely going to be a bad one.

At the Briones Regional Park, you can see the warning signs that have been put up for dog owners.

“Be cautious. Be aware. Because it could happen to you too,” dog owner Robert Newburne said.

Last month, Koa the dog was poisoned to death by a mushroom referred to as either a death cap or a death angel.

Koa ate the mushroom at Briones Regional Park in the East Bay while he was running around off leash.

Koa’s problems started one day after the park trip.

“So my wife came home and saw that there was blood in the stool,” Newburne said. “And he refused to eat.”

Newburne took Koa to an animal hospital and the news was devastating.

“They did some tests and came back to me within 20 minutes or so and had basically told me that his liver was destroyed,” Newburne said. “Basically, there wasn’t much they could do but they could try and save him.”

For two-and-a-half days, treatments worked, but two-and-a-half days after that, Koa passed.

Newburne says it has been a tough month but is now trying to warn other dog owners of the danger that has been created by the recent wet weather.

“And I have noticed an incredible amount of mushrooms out there…since that incident,” Newburne said. “My dog that survived and is still here and did not eat a mushroom will not be running free in any of the parks anymore. I go out to them. I love the parks, but she is now kept on a 20-foot leash where I can keep an eye on her.”

The vet that KRON4 talked with said this is much more common that you’d think.

She said she deals with between six and 12 cases like this every year.